The invention relates to a clamping wrench for hexagonal objects with an upper wrench jaw and a lower wrench jaw, which are respectively connected in a unitary manner to a limb of the handle, the wrench jaws being pivotably connected to each other in a longitudinally adjustable single joint.
Clamping wrenches of this type are known in various embodiments, as so-called water-pump wrenches with a serrated surface (DE 199 30 367 A1) and as so-called fittings wrenches with smooth clamping surfaces. On these, the lower wrench jaw and the upper wrench jaw have two surfaces disposed at an angle of 120° in relation to each other, with the result that hexagonal objects, in particular nuts, screw heads or union nuts of screwed pipe connections, can be received between the upper wrench jaw and the lower wrench jaw. Corners of the hexagonal object lying opposite one another are in each case at the deepest point of the two wrench jaws, the surfaces of which, disposed at 120° in relation to each other, lie against neighboring flank surfaces of the hexagonal object.
The longitudinally adjustable form of the single joint, which allows at least two, but in most cases more than two, relative positions of the two wrench jaws, makes it possible to receive hexagonal objects with different widths across flats.
However, it is only ensured that a hexagonal object is exactly received with the two wrench jaws lying against four flank surfaces of the hexagonal object if the fixable positions of the longitudinally adjustable single joint are chosen such that the two wrench jaws are aligned parallel to each other when the respective hexagonal object is received. In the case of all other hexagonal objects of different widths across flats, the wrench jaws are not aligned parallel to each other, with the result that only the two surfaces of one of the two wrench jaws, usually the upper wrench jaw, come properly to lie against neighboring flank surfaces of the hexagonal object, while the other wrench jaw, respectively, presses in an undefined way against the hexagonal object without lying flat against its surface. Consequently, a self-clamping action is not obtained; rather, the clamping force with which the hexagonal object is held between the wrench jaws must be applied manually by the user by means of a pincer action, in that he squeezes the two limbs of the handle together. For this purpose, the two limbs of the handle must be made adequately rigid and their angular position in every position for use must be such that the required clamping force can be applied manually.
In the case of fittings wrenches, which have smooth clamping surfaces (DE 195 18 555 C2), the clamping of the hexagonal object takes place only by means of the manually exerted closing force and not with a self-clamping action. This manual closing is sufficient, since in the case of the fittings concerned here the hexagonal objects are only screwed against elastic sealing material. These fittings wrenches often have a serrated single joint which is adjustable in small adjusting steps.
In the case of a known pipe wrench with serrated clamping surfaces (U.S. Pat. No. 6,026,714), which has an upper wrench jaw with a planar clamping surface and a stop and a lower wrench jaw with a convexly curved clamping cam surface, self-locking can only be achieved by the very short clamping surfaces formed by the individual serrations meeting the prerequisite required for self-locking, that the respective pivot point of the single joint lies on a perpendicular to the serration surface acting on the hexagonal object. Since, however, this self-clamping condition is satisfied only for the individual serration respectively acting directly on a corner of the hexagonal object, the entire clamping force is transmitted via this single serration in the immediate vicinity of the corner of the hexagonal object. The high local stressing which occurs leads to the hexagonal object being damaged if a relatively high torque is applied and/or the hexagonal object consists of low-strength material. In the case of hexagonal objects with rounded corners, self-clamping is no longer possible and further rounding and damaging of the hexagonal object is unavoidable.
Therefore, in the same way as in the case of serrated water-pump wrenches, in the case of such pipe wrenches a self-clamping action only occurs by chance and not reliably, via the serrations and in dependence on the respective formation of the corners of the hexagonal object. Therefore, there is the risk of the wrench slipping off and of injuries and accidents occurring.
Hexagonal objects with already rounded corners, for example already damaged nuts or screw heads, are further damaged by the wrenches slipping off, and therefore become unusable. The serrations of the clamping surfaces of the wrenches remove further material from the corners of the hexagonal objects. The wrench slips off completely. This damaging effect is further exacerbated by the fact that, to achieve a high torque, an increased clamping force is exerted on the wrench. As a result of the severe damage to the hexagonal object, it can no longer be loosened even with a self-clamping clamping wrench or with a rigid fixed wrench of the right size.
In the case of a known clamping wrench with smooth clamping surfaces aligned parallel to each other, the lower, movable wrench jaw is guided in a sliding manner with respect to the upper wrench jaw, which is rigidly connected to its part of the handle. A second part of the handle is mounted in a single joint which is adjustable along a serration arrangement and has a driving cam, which acts on the longitudinally displaceable lower wrench jaw. This known clamping wrench comprises more than three parts which are movable with respect to one another and is therefore of a relatively complicated construction and is thus costly to produce. With this clamping wrench, self-clamping is achieved with a force acting on the flank surfaces of the hexagonal object, but only with the great complexity and cost described. Furthermore, adjustability of the single joint with close graduation is required.
In addition, there are known self-clamping clamping wrenches for hexagonal objects (U.S. Pat. No. 4,651,597) in which a lower, convexly curved clamping surface presses the hexagonal object with a self-clamping action against the clamping surface of the upper wrench jaw. This upper wrench jaw is in this case not connected to a limb of the handle; its mounting on the lower wrench jaw is not longitudinally displaceable, with the result that adaptation to hexagonal objects of different sizes can take place only by changing the pivoting position of the upper wrench jaw. As a result, the range of use is restricted; use in a way similar to pincers is ruled out because of the absence of a second limb of the handle connected to the upper wrench jaw.